THE MUTATED Gh \ I 13 



type of the ascending allelomorphic series named -trap, an tiered, 

 ragged, snipped, notched, and nicked. 



It is important to note thai between 18 and 29 the temperature 

 effect was very small; a rise from 2<> to 30° affected the male wring 

 considerably; and from 30 to 31°, still more (three time- as 

 much)- In the female, the same happened bu1 began only 1° 

 higher. It oughl to be added thai general work in temperature 

 effects upon Drosophila proves thai 2!)° is aboul the upper limit 

 of the physiological temperature zone for this animal, beyond 

 which a rise in temperature has an effed upon developmental 

 processes thai in general terms may l>e described as inhibiting. 

 Stanley's work which led to the same results will he discussed in 

 the chapter on the sensitive period. 



A still more detailed account has been given by Riedel (1935). 

 She also concludes that the wing of a vg-f\y becomes more and 

 more like Wild type with the rise of temperature, and she finds 

 definite shapes characteristic for each temperature. Figure 3 

 (( n pages 14 and 15) shows such a series with the temperatures 

 used. Their resemblance to an allelomorphic series is obvious. 



In these experiments we are actually faeing the reciprocal of 

 the phenocopic effect, showing that at least in some cases the 

 process responsible for the development of the phenotype of a 

 mutation is reversible; furthermore, just as we found that the 

 phenocopies may be produced in a quantitative series imitating a 

 series of multiple allelomorphs, this reversed phenocopic action 

 also produces the phenotypes of the respective multiple allelo- 

 morphs of the ygf-series. \\ '<• shall return later to this very impor- 

 tant point. 



C. The Sensitive Period 



Half a century ago. the first workers in this field, studying 

 the temperature aberrations of butterflies, mainly with phylo- 

 genetic end- in view, made the important discovery that the 

 experiments were successful only if the stimulus was applied 



during a rather short period of larval life preceding pupation. 



This period was called the sensitive, or critical, period. All later 

 studies confirmed its existence and showed its importance 

 for an analysis of the problem. We shall describe the facts 



Using the same examples as before with the addition of new 

 cases. 



